The present invention relates to an abrasion-resistant coating applied to a metallic base material in a tip-end portion of a blade for a gas turbine, a gas turbine engine, a compressor, and the like, and a method for applying the abrasion-resistant coating.
A gap between the tip end of a blade for, for example, a gas turbine and a split ring fixed on the inner peripheral surface of a blade housing portion is required to be as small as possible to enhance the gas turbine efficiency by restraining a shortcut of gas to the downstream-side stage.
However, if the gap is too small, at the initial stage of operation start of gas turbine, due to thermal expansion of blade, decentering of rotor, vibrations of the whole of gas turbine, and thermal deformation etc. of the blade ring exposed to high-temperature gas by a long-term operation of gas turbine, the tip-end portion of blade comes into contact with a blade ring, whereby both or either one of blade, especially the tip end thereof is sometimes damaged excessively.
As a countermeasure against this problem, there has been proposed a technology in which an abrasion-resistant coating consisting of a material harder than the material forming the blade ring is applied at the tip end of blade. The aim of this technology is to keep the gap between the blade tip end and the blade ring to a minimum by grinding the surface of blade ring by the coating with the blade itself being scarcely damaged. A part of this technology has already been employed.
For example, Japanese Patent Provisional Publication No. 4-218698 (No. 218698/1992) and Japanese Patent Publication No. 8-506872 (No. 506872/1996) have disclosed an Mxe2x80x94Crxe2x80x94Alxe2x80x94Y (hereinafter referred to as MCrAlY, where M designates a metal element) matrix having a high oxidation resistance at a high temperature used as a bond coating. Also, there has been disclosed an abrasion-resistant coating in which cubic boron nitride (hereinafter referred to as CBN) particles having high hardness and high heat resistance are dispersed in the matrix as abrasive particles, and there has been a description such that the coating is applied by electrodeposition plating. Although this technology is said to have been completed technically, the apparatus and process for applying the coating is complicated, and a long period of time is required to complete the application work, which presents a problem of high cost.
Also, Japanese Patent Provisional Publication No. 11-222661 (No. 222661/1999) and Japanese Patent Provisional Publication No. 11-229810 (No. 229810/1999) have disclosed a bond coating consisting of MCrAlY, which has a high oxidation resistance at a high temperature. Also, there has been disclosed that an abrasion-resistant coating, in which abrasion-resistant layers consisting mainly of zirconia etc., which have high hardness and high heat resistance, are piled directly or via an alumina layer, is applied on the bond coating, and a part of the coating is applied by thermal spraying including plasma spray.
Further, Japanese Patent Provisional Publication No. 10-030403 (No. 030403/1998) has disclosed an abrasion-resistant coating in which alumina particles are fixed by a nickel-plated layer formed on the surface of base material and a nickel-based heat resisting alloy layer. Also, there has been a description such that this coating is applied by plating, thermal spraying, HIP treatment, and other means.
However, the above-described application method includes other coating means such as electrodeposition plating and EB-PVD in addition to thermal spraying, so that the operation is troublesome, and the cost is high. Moreover, it is difficult to control the distribution of hard particles having a high abrasion resistance, for example, because the hard particles are embedded in the bond coating, which presents a problem of poor grindability and insufficient heat resistance.
Besides, INDUSTRIAL DIAMOND REVIEW (4/99) describes an abrasion-resistant coating in which Ti coated CBN is brazed. Although brazing has an advantage of being easy in operation and low in cost, it has disadvantages in terms of oxidation resistance of bond coating formed thereby and long-term abrasion resistance (durability) (for example, CBN is separated due to the deterioration thereof).
The present invention has been achieved in view of the above situation, and accordingly an object thereof is to provide an abrasion-resistant coating which has high oxidation resistance and durability and can be applied easily at a low cost to solve the above problems with the conventional examples, and a method for applying the abrasion-resistant coating.
The abrasion-resistant coating in accordance with the present invention is formed of a bond coating formed on the surface of a metallic base material by melting of a mixture containing a brazing filler metal and MCrAlY and hard particles dispersed in and fixed to the bond coating so that some of them are partially protruded from the surface of the bond coating.
In the present invention, a metal coating for improving wettability relative to the brazing filler metal can preferably be formed on the surface of the hard particle.
Also, the abrasion-resistant coating can be formed of hard particles fixed to a metal plating layer provided on the surface of a metallic base material and a bond coating formed on the surface of the metallic base material by melting of a mixture containing a brazing filler metal and MCrAlY so that some of the hard particles are partially protruded from the surface of the bond coating. Further, a plurality of layers in which a plurality of kinds of hard particles having different hardness and oxidation resistance are dispersed separately can be formed, and further, in each of the layers, a metal plating layer for fixing hard particles dispersed in that layer can be formed between the layers. Also, the method for applying the abrasion-resistant coating in accordance with the present invention includes a step of applying a liquid substance containing metal coated hard particles, a brazing filler metal, MCrAlY, and a liquid binder which evaporates at the time of heating to the surface of a metallic base material and a step of heating the applied liquid substance locally to a brazing temperature under high vacuum to evaporate the binder and to melt the brazing filler metal and MCrAlY. Further, the method for applying the abrasion-resistant coating in accordance with the present invention includes a step of affixing a sheet consisting of a plastic mixture containing a brazing filler metal, MCrAlY, and a binder which evaporates at the time of heating to the surface of a metallic base material, a step of applying a liquid mixture consisting of hard particles H and the binder to the affixed sheet, and a step of heating the affixed sheet and applied liquid mixture locally to a brazing temperature under high vacuum to evaporate the binder and to melt the brazing filler metal and MCrAlY.
The method for applying the abrasion-resistant coating in accordance with the present invention includes a step of forming a metal plating layer on a metallic base material and temporarily fixing hard particles to the plating layer, a step of pouring a liquid mixture containing a brazing filler metal, MCrAlY, and a liquid binder which evaporates at the time of heating onto the metal plating layer, and a step of heating the poured liquid mixture locally to a brazing temperature under high vacuum to evaporate the binder and to melt the brazing filler metal and MCrAlY.
In these inventions, a plurality of coating layers in which a plurality of kinds of hard particles having different hardness and oxidation resistance are dispersed separately can be formed successively, and further in each layer of the plural coating layers, a metal plating layer for fixing the hard particles dispersed in the layer can be formed.